In a plasma processing apparatus including a chamber and an ICP (inductively coupled plasma) antenna disposed outside the chamber, a ceiling portion of the chamber which faces the ICP antenna is configured as a window member (dielectric window) made of a dielectric material, e.g., quartz or the like. The ICP antenna is connected to a high frequency power supply, and magnetic force lines are generated at the ICP antenna by a high frequency current supplied to the ICP antenna. The generated magnetic force lines are transmitted through the dielectric window, thereby generating a magnetic field in the chamber along the ICP antenna. If the magnetic field is temporally changed, an induced electric field is generated. Electrons accelerated by the generated induced electric field collide with molecules or atoms of a processing gas introduced into the chamber, thereby generating a plasma. Since the induced electric field is generated along the ICP antenna, the plasma is also generated in the chamber along the ICP antenna.
Here, the dielectric window partitions the inside of the chamber which is a depressurized environment and the outside of the chamber which is an atmospheric environment, and therefore, it is required to have a thickness that ensures stiffness enough to endure the pressure difference. Further, a substrate to be subjected to plasma processing while being accommodated in the chamber, e.g., a semiconductor wafer or a glass substrate for use in FPD (flat panel display), is expected to be further scaled up, so that the dielectric window opposite to the substrate also needs to be scaled up. At this time, if the thickness of the dielectric window is increased to ensure stiffness required in the case of scaling up the dielectric window, the distance between the ICP antenna and the substrate is increased, which results in deterioration of efficiency. Moreover, the increase in the weight of the dielectric window leads to the increase in the apparatus weight or the increase in costs.
Accordingly, there is suggested a configuration in which a ceiling portion of a chamber is configured as a conductive window made of a material of low cost and high stiffness, e.g., metal (see, e.g., Japanese Patent Application Publication No. 2011-029584.) In the conductive window, the magnetic force lines are shielded by the metal, so that slits penetrating through the conductive window are provided and the magnetic force lines pass through the slits. However, the number or the size of the slits provided at the conductive window is restricted. Therefore, in the case of employing the conductive window, there occurs a problem that the transmission efficiency of the magnetic force lines deteriorates and as a result, the plasma generating efficiency deteriorates.
Meanwhile, there is suggested a configuration in which a ring-shaped conductor is disposed near an inductive antenna including an inner coil and an outer coil along the inductive antenna (see Japanese Patent Application Publication No. 2011-103346.) Here, the mutual inductance is controlled at circumferential positions between the ring-shaped conductor and the induction antenna and between the ring-shaped conductor and the plasma by changing the radius of the ring-shaped conductor from the center of the apparatus and the cross-sectional shape of the ring-shaped conductor depending on the circumferential angle of the coils. Accordingly, the coil current varied depending on the circumference of the coils of the induction antenna can be compensated, and uniformity of a current on the generated plasma in the circumferential direction can be improved. With such a configuration, the deterioration of the plasma generating efficiency can be suppressed.
However, the aforementioned conventional configuration cannot sufficiently improve the plasma generating efficiency, and a higher efficiency is required.